NZ228101A

NZ228101A - Solvent extraction process for extracting palladium

Info

Publication number: NZ228101A
Application number: NZ228101A
Authority: NZ
Inventors: Raymond Frederick Dalton; Arthur Burgess
Original assignee: Ici Plc
Priority date: 1988-03-09
Filing date: 1989-02-22
Publication date: 1990-06-26
Also published as: FI96326C; FI96326B; DE68903969D1; EP0332314A3; NO890995L; CN1025556C; CN1035851A; ES2053974T3; JPH0448482B2; AU608123B2; FI891125A0; NO890995D0; EP0332314B1; NO174972C; EP0332314A2; AU3022189A; CA1337738C; US4961856A; DE68903969T2; JPH01297101A

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number £28101 \ :w^9: Cwiiyiciw w-pscrft. 3l'on FticcJc CNr«j- W*Bil/0>S la;**!: . «?#£/<? Publication Date: . ■26.-JUN-1990" P.O. Joumai, No: . da-. 22 8 NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION SOLVENT EXTRACTION PROCESS ■jA/We, IMPERIAL CHEMICAL INDUSTRIES PLC, a British company of, Imperial Chemical House, Millbank, London SW1P 3JF, United Kingdom hereby declare the invention for which^ / we pray that a patent may be granted torjaaB/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - (followed by page 1A) A 22 8 1 0 1 1A S.34667 SOLVENT EXTRACTION PROCESS The present invention relates to a solvent extraction process and, in particular, to such a process which is capable of 5 extracting palladium, especially separating palladium from platinum. The use of solvent extraction techniques to separate wanted metal values from other metals has been known for many years and such techniques are being practised commercially for the separation of certain metals such as copper. Solvent extraction processes have 10 been proposed for the separation of platinum and palladium. One process developed by the National Institute for Metallurgy (NIM) is described in Proc. International Solvent Extraction Conference, 1977, at pages 24 to 31. In the NIM process, platinum and palladium are separated from other metals by extraction using an amine type 15 extractant and are stripped from the extractant using hydrochloric acid. The palladium is then separated from the platinum by solvent extraction using alkyl sulphides, particularly di-n-hexyl sulphide, as the extractant. The palladium may then be stripped from the extractant using ammonia as the ligand. Whilst the extractant is 20 indicated to have a high capacity for palladium, it is stated that the kinetics of extraction are quite slow and that a typical contact time for complete extraction will be between one and three hours. An alternative procedure is described in Extraction Metallurgy, 1981, pages 34 to 41. According to this alternative procedure, 25 palladium is extracted using hydrqxyoximes, particularly the beta-hydroxyoximes. However, the extraction rate is reported to be slow and equilibration times of greater than three hours are indicated to be needed. Stripping of the palladium into a strip solution is also slow. In commercial operation it is desirable that 30 extraction occurs quickly and equilibration times of several hours are not desirable. It is an object of the present invention to provide a solvent extraction process for the extraction of palladium. It is a further object of the invention to provide a solvent extraction 22 8 1 0 1 2 S.34667 process for the separation of palladium and platinum. It is a yet further object of the present invention to provide a solvent extraction process in which a useful separation can be achieved in a relatively short time. 5 According to the present invention there is provided a solvent extraction process for extracting palladium values from aqueous solutions of palladium salts containing halide or pseudo halide anion which comprises the steps of (1) contacting the aqueous solution containing palladium salts with a solution of an extractant 10 in a water-immiscible organic solvent; (2) separating the aqueous solution from the solution of the extractant in the water-immiscible solvent into which palladium has been extracted; and (3) contacting the resultant organic phase with an aqueous strip solution whereby the palladium transfers into the aqueous strip solution characterised 15 in that the aqueous solution of palladium salts containing halide or pseudo halide anion is contacted with a solution in a water-immiscible organic solvent of an extractant which is a substituted heterocyclic compound containing a single heterocyclic ring containing 1, 2 or 3 nitrogen ring atoms and one or more groups 20 -COX which are linked directly to the heterocyclic ring or are linked to the heterocyclic ring through a group A wherein A is an optionally substituted methylene linking group, an optionally substituted vinylene linking group or an optionally substituted phenylene linking group; 1 2 3 25 X is a group -OR or -NR R ; .1 is a hydrocarbyl group or substituted hydrocarbyl group containing from 5 to 36 carbon atoms; and 2 3 R and R which may be the same or different, are hydrogen or a hydrocarbyl group or a substituted hydrocarbyl group, and 2 3 2 3 30 in each group -NR R , R and R together contain from 5 to 36 carbon atoms. The aqueous solution of palladium salts may also include salts of other metals. The solution may be obtained from a palladium-containing catalyst and may include other metals also 22 8 1 3 S.34667 contained in the catalyst or which are contaminants of the catalyst. Alternatively, the aqueous solution may be a solution containing platinum group metal salts. The term "platinum group metal" as used herein refers to 5 those metals in Group VIII of the Periodic Table which are in the fifth and sixth periods. Thus, the platinum group metals are platinum, palladium, ruthenium, rhodium, osmium and iridium. Typically, ores containing platinum group metals also contain other Group VIII metals such as iron and nickel. The.ore may also contain 10 other metals for example metals of Group IB of the Periodic Table such as copper, silver and gold. All references herein to the Periodic Table are to the Short Periodic Table as set out on the rear inside cover of "General and Inorganic Chemistry" by J.R.Partington, Second Edition, published in 15 1954 by MacMillan and Co.Ltd., London. The term "pseudo halide" is used herein to mean those compounds which show a resemblance to the halogens in their reactions and in the properties of their compounds and include cyanogen, oxy-, thio- and seleno-cyanogen and the azide radical. 20 The substituted heterocyclic compound may be of the general type Het [(A) (COX) ] a y n 25 where A and X are as hereinbefore defined; Het is, or contains, a single heterocyclic ring containing 1, 2 or 3 nitrogen ring atoms and the group or groups -(A)a(C0X)^ are linked to the ring atoms of the heterocyclic ring; a is 0 or 1; 30 n is at least one up to the maximum number of free valencies in the heterocyclic ring; and y is from 1 up to 3. By the term "free valencies" is meant those valencies of the heterocyclic ring atoms which are not used in forming the ring. 22 8 1 4 S.34667 Any free valencies which are not occupied by a group -(A)a(COX)^ are occupied either by a hydrogen atom or a substituent group (Y) which is selected from halogen, alkyl, aryl, alkoxy, aryloxy, aralkyl, alkaryl, cyano, nitro or carboxylic acid. 5 The group Het is a single heterocyclic ring which may be fused with a non-heterocyclic ring, for example a benzene ring as in a benzimidazole compound. In such a fused ring compound, the benzene ring may be unsubstituted, other than by the heterocyclic ring, or may be substituted by the groups Y, as hereinbefore defined. 10 In the substituted heterocyclic compound, if the hydrocarbyl 12 3 groups R , R and R are substituted the substituents are one or more of halogen, for example chlorine, nitro, cyano, hydroxy, alkoxy, aryloxy, alkoxycarbonyl and alkylcarbonyloxy. The group Het may be a pyridine, pyrimidine, pyrazine, 15 pyridazine or 1,2,4-triazole ring or may be a fused ring system such as a benzimidazole system. If the substituted heterocyclic compound is one containing at least two COX groups, the substituent -X in each of the respective groups -COX may be the same or different. Thus, for example, when n 4 5 20 is two, the two groups -COX may be -COOR and -COOR respectively 4 5 where R and R are different and are both hydrocarbyl groups containing from 5 to 36 carbon atoms. Similarly, if two groups -COX 1 2 3 are present, the two groups -COX may be -COOR and -CONR R respectively. 25 If the substituted heterocyclic compound contains a group A, this is preferably a vinylene linking group which contains no substituents other than the groups -COX, and is particularly a vinylene linking group which contains two groups -COX, one on each carbon atom of the vinylene linking group. 30 In the substituted heterocyclic compounds which can be used in the process of the present invention, when the group X is OR , the group R may be an alkyl group or a substituted alkyl group and is preferably an alkyl group, particularly an alkyl group containing from 8 to 24 carbon atoms such as, for example an octyl, nonyl, 22 8 1 S.34667 decyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl or octadecyl group. Alternatively, and generally less preferably, the group may be a cycloalkyl group such as cyclohexyl; or an aralkyl group 5 such as benzyl; or an aryl or alkylaryl group such as phenyl, p-nonylphenyl or p-dodecylphenyl. If the substituted heterocyclic compound is one.in which a single group -COX is linked directly to the heterocyclic ring and no substituent groups Y are present, the group R* is preferably a 10 branched chain alkyl group containing from 9 to 24 carbon atoms. The group R* may be an isomeric mixture of groups containing the same number of carbon atoms or a mixture of groups containing different numbers of carbon atoms (which may themselves be an isomeric mixture), for example a mixture of different alkyl groups. If R is 15 a mixture of groups containing different numbers of carbon atoms, the average number of carbon atoms is preferably from 9 to 24. Very conveniently the group R may be a highly branched group such as is obtained by the reaction of the corresponding heterocyclic carboxylic acid with an alcohol prepared by the Guerbet 20 and Aldol condensations. Such alcohols are characterised by branching at the position beta to the hydroxyl group, and have the general formula: 25 HO - CH2 - CH R6 ^R7 where R^ and nJ are alkyl groups and may be the same or different. In general R^ contains 2 fewer carbon atoms than R , and groups R 30 derived from these alcohols include for example, 22 8 1 0 1 S.34667 CH2 - CH •C6H13 'C8HI7 CH2 - CH. 10 C8H17 C10H21 15 - CH2 - CH' 30 C7H15 C H 9 19 The groups and R7 may be straight chain or branched chain 20 alkyl groups and may be isomeric mixtures of alkyl groups. A mixture of highly branched alcohols may be obtained by Guerbet or Aldol condensations of mixtures of alcohols and aldehydes respectively. An ester, especially a monoester, having a useful solubility 25 in the water-immiscible organic solvent is obtained from an alcohol which is the product of the dimerisation of commercial nonanol (3,5,5-trimethylhexanol). In such an ester the group R^ is believed to consist essentially of a mixture of geometrical isomers of a radical of the formula: I CH, CH CH. CH, CH, I 3 | 3 | 2 | 3 | 3 CH - C - CH - CH - CH - CH. - CH„ - CH - CH - C - CH 3 | 2 2 2 2 i 3 CH CH 3 3 35 22 8 1 S.34667 If the substituted heterocyclic compound is a diester, each group R may be any of those groups R^ listed previously. In the diesters, the groups R are conveniently the same and are preferably straight chain or branched chain alkyl groups. When the substituted 5 heterocyclic compound is a diester, we have obtained useful results when the groups R together contain a total of from 16 to 36 carbon atoms. The groups R* may contain a mixture of isomers, for example a mixture of nonyl isomers derived from isononanol obtained by the hydroformylation of a mixture of octenes, a mixture of decyl isomers 10 obtained from isodecanol, or a mixture of tridecyl isomers obtained from tridecanol. If the substituted heterocyclic compounds used in the process of the present invention are amides, that is the group X is 2 3 2 3 2 the group -NR R , the group -NR R may be a secondary (R is 2 3 15 hydrogen) or a tertiary group. The groups R and R , which may be the same or different, may be groups of the type indicated previously 1 2 3 2 3 for the group R . In each group -NR R , R and R taken together 2 contain from 5 to 36 carbon atoms. Thus R may be, for example, a 3 lower alkyl group, for example a methyl group, provided R is 2 3 20 correspondingly larger. It is particularly preferred that R and R taken together are alkyl groups containing a total of 15 to 36 carbon 2 3 atoms. If the group -NR R is a tertiary group, sufficient solubility in preferred water-immiscible organic solvents may 2 3 generally be achieved if R and R are straight chain or branched 2 3 2 25 chain alkyl groups. However if -NR R is a secondary group (R is 3 hydrogen), R is preferably a branched chain alkyl group. When n is 2 3 two, and all of the groups R and R are alkyl groups, the total number of alkyl carbon atoms preferably does not exceed 70, for example the total number of alkyl carbon atoms is preferably from 20 30 to 70. As a more specific aspect of the present invention there is provided a solvent extraction process for extracting palladium values from aqueous solutions of palladium salts containing halide or pseudo halide anion which comprises the steps (1) to (3) described herein, 8 22 8 1 0 1 S. 34667 characterised in that the aqueous solution of palladium salts containing halide or pseudo halide anion is contacted with a solution in a water-immiscible organic solvent of an extractant which is a substituted pyridine of formula: 5 COX where X and Y are both as hereinbefore defined; and x is zero or an integer from 1 up to 4. 15 Preferably the substituted pyridine is one in which x is zero. As a yet further aspect of the present invention there is provided a solvent extraction process for extracting palladium values from aqueous solutions of palladium salts containing halide or pseudo halide anion which comprises the steps (1) to (3) described herein 20 characterised in that the aqueous solution of palladium salts containing halide or pseudo halide anion is contacted with a solution in a water-immiscible organic solvent of an extractant which is a substituted pyridine of formula: 25 (COX) n 30 wherein 1 2 3 X is a group -OR or -NR R ; n is 2 or 3; each R* which may be the same or different, is an alkyl group and together the groups R^ contain a total of from 16 35 to 36 carbon atoms; 22 8 1 0 1 9 S.34667 2 3 each R and R which may be the same or different, is an alkyl group and the total number of alkyl carbon atoms contained 2 3 in all the respective groups R and R is from 20 to 70; 5 z is zero or an integer from 1 up to (5-n); and each Y which may be the same or different, is one or more of the substituents halogen, alkyl, aryl, alkoxy, aryloxy, aralkyl, cyano, nitro or carboxylic acid. 10 When z has a value of at least one, the pyridine ring carries substituent(s) in addition to the group(s) -COX. The substituent may be a carboxylic acid group, and the process of the present invention includes the use, for example, of a half ester of a pyridine dicarboxylic acid. 15 The substituted pyridine compounds which can be used in the process of the present invention are disclosed in European Patent Specification No.0057797, which also discloses processes for the preparation of these substituted pyridine compounds and also the use of such compounds as extractants of copper values from an aqueous 20 solution of a copper salt containing halide or pseudo halide. Substituted pyridine compounds which can be used in the process of the present invention can be prepared by the procedures described in more detail in European Patent Specification No.0057797, the disclosure of which is incorporated herein by reference. 25 Substituted pyridine compounds which can be used in the process of the present invention include those in which the value of n is one and examples of such compounds include the esters and amides of nicotinic, isonicotinic and picolinic acids. Other compounds which can be used include those in which the value of n is two such 30 as the bis esters or bis amides of the pyridine diacids including pyridine-2,4-dicarboxylic acid, pyridine-2,5-dicarboxylic acid and pyridine-3,5-dicarboxylic acid. When the value of n is three, the substituted pyridine compound may be a tris-ester or tris amide of a pyridine triacid such as pyridine-2,4,6-tricarboxylic acid. A 22 8 1 10 S.34667 mixture of compounds may be used such as a mixture of esters and amides or a mixture of bis-esters or bis-amides of isomeric pyridine-dicarboxylic acids. Alternatively, the substituted pyridine compound may be one derived from a di- or tri-carboxylic 5 acid and containing both ester and amide groups. substituted heterocyclic compound may be one in which the heterocyclic group is a ring containing two nitrogen atoms as in the pyrimidine, pyrazine and pyridazine derivatives of the following 10 formulae: According to a further aspect of the present invention, the (i) 15 or 20 (COX) n (ii) or 25 (COX) n 30 wherein X and Y are as hereinbefore defined; n is 1, 2 or 3; and b is zero or an integer from 1 up to (4-n). 22 8 1 0 1 11 S.34667 The 5 to 36 carbon atoms which are present in the groups R 2 3 or R and R are preferably alkyl carbon atoms. The group Y may be a substituent containing one or more alkyl carbon atoms, in which 12 3 case the number of alkyl carbon atoms present in R or R and R may 12 3 5 be reduced accordingly provided R or R and R contain at least 5 carbon atoms. Preferably at least one position ortho to one of the two nitrogen atoms in the pyrimidine, pyrazine or pyridazine ring is free from bulky substituents and preferably is free from any substituent. 10 It is especially preferred that both positions ortho to at least one of the nitrogen atoms are free from bulky substituents, and preferably are free from any substituent. There is thus a general preference that one of the two nitrogen atoms in the pyrimidine, pyrazine or pyridazine ring is sterically unhindered, whilst the 15 other nitrogen atom is sterically hindered by one or more adjacent substituents. As noted previously herein, when n is 2 or 3, the substituent -X in the respective groups -COX may be the same or different. As examples of suitable pyrazines wherein n is 2, there 20 may be mentioned alkyl esters of 2,6-dicarboxypyrazine. As examples of suitable pyrimidines wherein n is 2, there may be mentioned alkyl esters of 4,5-dlcarboxypyrimidine. As examples of suitable pyridazines wherein n is 2 there may be mentioned alkyl esters of 4,5-dicarboxypyridazine. 25 When n is 1, the group -COX is preferably located in the -5 position in the pyrimidine ring, since we have found that such compounds generally have superior hydrolytic stability. In the pyrazine ring the substituent -COX will be in a position adjacent to one of the nitrogen atoms. 30 The group, or groups, -Y if present are preferably one or more alkyl groups, for example one or more lower alkyl groups or are one or more optionally substituted aryl groups. As optionally substituted aryl groups there may be mentioned the phenyl group and the phenyl group carrying as optional substituent one or more lower 22 8 1 0 1 12 S.34667 alkyl groups or lower alkoxy groups or one or more halogen atoms or one or more carboxylic acid or carboxylic acid ester groups. The presence of, for example an alkyl substituent, on the aryl group may provide enhanced solubility of the reagent in the water-immiscible 5 organic solvent or may permit the use of a relatively shorter alkyl chain in the group -OR*'. Pyrimidine compounds which can be used in the process of the present invention and which have the group -COX in the preferred -5 position, preferably have a substituent -Y in the -4 (or the 10 equivalent -6) position, thereby increasing the steric hindrance of the nitrogen in the -3 (or the equivalent -1) position. Similarly, the substituted pyrazine compounds may have a substituent -Y in the -6 position to hinder the reactivity of the nitrogen in the -1 position, thereby favouring the formation of a 15 metal complex through the nitrogen in the -4 position. The substituted pyrimidine, pyrazine and pyridazine compounds which can be used in the process of the present invention are disclosed in European Patent Specification 0112617, which also discloses processes for the preparation of these substituted 20 compounds and also the use of such compounds as extractants of copper values from an aqueous solution of a copper salt containing halide or pseudo halide. Substituted pyrimidine, pyrazine and pyridazine compounds which can be used in the process of the present invention can be prepared by the procedures described in more detail in 25 European Patent Specification 0112617, the disclosure of which is incorporated herein by reference. In the substituted pyrimidine, pyrazine and pyridazine compounds the group R may be derived from a primary alcohol, which is preferably a branched chain primary alcohol but, for the pyrazine 30 compounds especially, there may be advantages in employing a group R derived from a branched secondary or tertiary alcohol, such as for example 3,9-diethyltridecan-6-ol. As yet a further aspect of the present invention, the substituted heterocyclic compound may be one in which the 22 8 1 13 S.34667 heterocyclic group is a 1-substituted 1,2,4-triazole as in compounds of the formula: N N - (A) (COX) a m u where A, X, a and m are all as hereinbefore defined. When a in the preceeding formula is 0, m will be 1 and the 10 substituted triazole is a derivative of respective formulae: N N - COOR1 u ■N 15 and N N - C0NR2R3 20 u When a is 1 and A is a methylene group, the 1-substituted 25 triazoles have the formula: N N - CH - (COX) (3-m) m 30 U wherein m is from 1 to 3 and X is as hereinbefore defined, and wherein any hydrogen atoms not replaced by a -COX group may be replaced by an optical substituent such as a halogen atom, cyano group, nitro group or lower alkyl group. We have found that when 22 8 1 14 S.34667 m is 3, the compounds generally have reduced hydrolytic stability, and it is preferred that m is 1 or 2. When m is 2, the compound is found to show a good balance of properties as between hydrolytic stability and reagent "strength" as discussed below. 5 The term "lower alkyl group" as used herein indicates an alkyl group containing from 1 to 4 carbon atoms. When a is 1 and A is an optionally substituted vinylene linking group, the triazole typically has the formula: 0 A1 A2 I I N N - C = C - COX 15 1 2 wherein X has the meaning given previously and A and A are hydrogen or optional substituents such as a halogen atom (for example a fluorine or chlorine atom), cyano group, nitro group or a lower alkyl group or the group -COX. A useful extractant of this type is one in 1 2 20 which A is a group -COX, A is hydrogen and X is the same in both groups COX. Compounds of this type have good hydrolytic stability. To achieve good solubility of the compound in preferred 12 3 water-immiscible organic solvents, R , R and R respectively are preferably branched alkyl groups or a mixture (including an isomeric 25 mixture) of branched alkyl groups. It has been found that certain branched chain groups also provide improved hydrolytic stability. The 1-substituted-l,2,4-triazoles of the present invention may be prepared by conventional means. For example the (hydrocarb)oxycarbonyl derivatives wherein X is OR and a is 0 may be 30 prepared by the reaction of a hydrocarbyl chloroformate, derived from the corresponding hydrocarbyl alcohol, R OH, with 1,2,4-triazole. If a is 1, the compounds may be prepared by reaction with the alcohol R OH with the acid: 22 8 1 0 1 15 S.34667 N N - A - CO - OH U 5 or with the acid hydride thereof. It has been found that compounds having a high degree of branching at the positions in the vicinity of the carbonyl group generally show an improved resistance to hydrolysis under the 10 stringent conditions employed in the solvent extraction process. For example for l-(hydrocarb)oxycarbonyl derivatives wherein X is -OR , a high degree of branching at the position in the vicinity of the carbonyl group may be obtained for example by using a secondary alcohol as starting material. Suitable secondary alcohols 15 may be prepared for example by the procedures described by Pearce, Richards and Scilly in J.Chem.Soc. (Perkln I), 1972 pp.1655 to 1669. We have found for example that a product prepared from such a secondary alcohol has a higher hydrolytic stability than a product obtained from a primary alcohol. 20 l-substituted-l,2,4-triazoles which can be used in the process of the present invention are disclosed in UK Patent Specification 2150133, which also discloses processes for the preparation of these substituted compounds and also the use of such compounds as extractants of copper values from an aqueous solution of 25 a copper salt containing halide or pseudo halide. 1-substituted-1,2,4-triazole compounds which can be used in the process of the present invention can be prepared by the procedures described in more detail in UK Patent Specification 2150133, the disclosure of which is incorporated herein by reference. 30 As a yet further aspect of the present invention, the substituted heterocyclic compound may be one in which the heterocyclic group is, or contains, a diazole ring as in a N-substituted 1,3-diazole compound of formula: 22 8 1 Of 16 S.34667 Z D .N I COX 5 wherein X is as hereinbefore defined; 8 R is hydrogen or an optionally substituted lower alkyl group or an optionally substituted vinyl group; and 10 D and Z, which may be the same or different, are separately hydrogen, an optionally substituted hydrocarbon group, a halogen, a nitro group, a cyano group or a carboxylic ester group, or where D and Z both together with the two carbon atoms joining them form an optionally substituted aromatic or aliphatic cyclic group. 15 As diazole compounds which may be used in the present invention there may be mentioned benzimidazoles of formula: 20 / COX imidazoles of formula 25 COX 30 17 22 S.34667 01 and tetrahydrobenzimidazoles of formula: g wherein D, R , X, Y and Z are all as hereinbefore defined; and 10 c is zero or from 1 up to 3. In the tetrahydrobenzimidazole, it is preferred that Y, if present, is a hydrocarbyl group. The number of substituents Y is preferably zero, one or two. 8 R is preferably hydrogen, as it has been found that such 15 compounds generally have a suitable strength of ligand and a better selectivity for metal over acid (as will be discussed later). It is preferred that the total number of alkyl carbon atoms in all substituents of the diazole compound is from 9 to 30 and preferably from 14 to 30, since the solubility of the compound in 20 suitable water-immiscible organic solvents may be undesirably low if the total number of saturated carbon atoms is less than 14, whilst the disengagement of the organic and aqueous phases during the solvent extraction may be undesirably slow if the total number of alkyl carbon atoms exceeds 30. 25 In the group -COOR , the group R is preferably an alkyl group, but may alternatively be a cycloalkyl group such as cyclohexyl, an aryl, an alkylaryl or an alkoxyaryl group. To achieve good solubility of the compound in preferred water-immiscible organic solvents, R* is preferably a branched alkyl 30 group or a mixture (including an isomeric mixture) of branched alkyl groups. If R is an aralkyl or alkoxyaryl group, the alkyl portion of the group is preferably a branched alkyl group or a mixture (including an isomeric mixture) of branched alkyl groups. The hydrocarbyl group R in the heterocyclic compound is preferably an 22 8 1 18 S.34667 alkyl group and the preferred number of alkyl carbon atoms in the group R depends on the total number of alkyl carbon atoms In the g other substituents of the diazole compound. If R is hydrogen or methyl and the substituted heterocyclic compound is a benzimidazole 5 compound whose substituent(s) Y together contain either no alkyl carbon atoms or at most one alkyl carbon atom, or there is used an imidazole whose substituents D and Z together contain either no alkyl carbon atoms or at most one alkyl carbon atom, or there is used a tetrahydrobenzimidazole whose substituent(s) Y together contain 10 either no alkyl carbon atoms or at most one alkyl carbon atom, then in each case it is preferred that R contains from 9 to 24 carbon atoms. Compounds for use in the process of the present invention wherein -COX is the group -CO.OR1 may be prepared for example from 15 the alcohol R*OH by treatment with phosgene to give the chloroformate compound R^O-CO.Cl which may be reacted with the appropriate imidazole, benzimidazole or tetrahydrobenzimidazole to give the desired product. Good solubility in preferred water-immiscible organic 20 solvents is conferred on the substituted diazole compounds when R is derived from commercial isooctadecanol prepared as previously described herein. It has been found that compounds having a high degree of branching, and especially compounds having a high degree of branching 25 at the position adjacent to the carbonyl function in the group -COOR show an improved resistance to hydrolysis under the stringent conditions employed in the solvent extraction process. As noted previously herein the group -CO.OR may be prepared by the reaction of the alcohol and phosgene to form the chloroformate 30 which is reacted with a diazole compound. In this reaction, the use of a primary alcohol such as isooctadecanol having a high degree of branching at the carbon atom adjacent to the -C^OH group gives rise to a product in which the highly branched group is separated from the carbonyl function by the -CH^- group. Such products have superior 22 8 1 0 19 S.34667 hydrolytic stability as compared with the corresponding unbranched compound but further improvements in hydrolytic stability may generally be obtained by using a secondary alcohol R*OH, for example 3,9-diethyl-tridecan-6-ol as starting material. Such a secondary 5 alcohol provides the branching in a position directly adjacent to the carbonyl function. The diazoles for use in the present invention wherein -COX 2 3 is the group -CO.NR R may be prepared by conventional means, for example by treatment of the appropriate benzimidazole, imidazole or 10 tetrahydrobenzimidazole with an alkyl isocyanate in the presence of a catalyst such as dibutyltin dilaurate. N-substituted-1,3-diazoles which can be used in the process of the present invention are disclosed in European Patent Specification 0193307, which also discloses processes for the 15 preparation of these substituted compounds and also the use of such compounds as extractants of metal values, particularly copper and zinc, from an aqueous solution of a metal salt containing halide or pseudo halide. N-substituted-1,3-diazole compounds which can be used in the process of the present invention can be prepared by the 20 procedures described in more detail in European Patent Specification 0193307, the disclosure of which is incorporated herein by reference. The process of the present invention can be used for the solvent extraction of palladium from aqueous solutions containing halide or pseudo halide anions in the presence of a range of other 25 metals. The aqueous solution may contain palladium values extracted from a palladium-containing catalyst and may also contain any other metals present in the catalyst, either as components or contaminants, and which are extracted with the palladium. 30 Alternatively, the aqueous solutions which can be used in the process of the present invention may be obtained by digesting, with aqua regia, an ore containing precious metals such as gold, silver and the platinum group metals, subsequently boiling off the nitric acid and adding ammonia to the residual solution. Some of 22 8 1 01 m 20 S.34667 the metal values are precipitated during this treatment and are filtered off before the solvent extraction process is effected. The ores containing platinum group metals are typically complex and contain varying proportions of a range of metals. The ore may be 5 digested and subjected to few or many intermediate stages before being subjected to the solvent extraction process of the present invention. Hence, the aqueous solution which is used in the solvent extraction process may be one from which at least some of the metals present in the ore have already been separated. It is a particular 10 aspect of the process of the present invention that it is effective in separating palladium from platinum. Hence, the aqueous solution which is treated in accordance with the present invention typically contains palladium and platinum and may contain other metals which may be platinum group metals or other constituents of the ore 15 including copper and nickel. We have found that the solvent extraction process of the present invention removes palladium from the aqueous phase into the organic phase containing the substituted heterocyclic compound but, with the exception of any copper which is present in the aqueous 20 solution, only minor proportions of the other metals present in the aqueous solution are extracted. If copper is present in the aqueous solution, a substantial proportion of the copper is extracted into the organic phase together with the palladium. The organic phase is separated from the original aqueous solution and may then be 25 selectively stripped to recover copper and palladium, essentially free of the other metal. Thus, according to a particular aspect of the present invention the aqueous solution contains platinum group metals and copper and is subjected to stages (1) and (2) wherein stage (3) is 30 effected in two steps, and in the first step (a) the organic phase is contacted with water or a dilute aqueous acid and in the second step (b) the residual organic phase is contacted with an aqueous ammonia solution. 22 8 1 o 21 S.34667 In step (3b), the residual organic solution is contacted with an aqueous ammonia solution which is typically a solution having an ammonia content of 2 to 20% w/v, especially 5 to 15% w/v. We have found that, in the foregoing process, in step (3a) 5 copper is stripped from the organic phase into the aqueous phase to give an organic phase which is essentially free of copper and an aqueous phase which is essentially free of palladium. In step (3b), essentially all of the palladium is stripped from the organic phase, the residual levels of copper and palladium in the stripped organic 10 phase being typically less than 5 and 50 ppm by weight respectively. Hence, the process of the present invention can be used to extract and separate copper and palladium values from an aqueous solution containing platinum group metals and copper. The extracted and separated palladium and copper are present in aqueous solution 15 from which the palladium, and the copper if desired, can be recovered using known techniques. More specifically, the aqueous solution from step (3a) may be electrolysed to recover copper. The aqueous solution from step (3b) may be treated to recover palladium, for example by the precipitation of an ammonia palladium chloride 20 complex. The aqueous solutions containing the platinium group metal salts contain palladium and platinum and typically contain at least one of copper, gold, rhodium, ruthenium, iridium, lead, nickel, iron and silver. The substituted heterocyclic compound is selective and 25 extracts copper and palladium but the other metals are extracted only at levels of a few ppm by weight, that is less than 20 ppm by weight and typically not more than 10 ppm by weight. The levels of the metals present in the aqueous solution can vary in dependence on the composition of the original ore and also on any intermediate steps to 30 which the solution has been subjected. Metals such as copper, palladium, nickel and iron are typically present in the solution at a concentration of at least lg/dm3 of solution and may be present at concentrations in excess of 10g/dm3, for example up to about 100g/dm3 although such high concentrations are typically achieved only with 22 8101 22 S.34667 copper. Other metals such as rhodium and lead may be present at a concentration of at least 100 mg/dm3 up to about 5g/dm3. Ruthenium may be present at a concentration of from about 20mg/dm3 up to about 600mg/dm3. Other metals which may be present include platinum, 5 gold, iridium and silver and these are typically present at concentrations between 10mg/dm3 and 100mg/dm3. The aqueous solution typically contains halogen or pseudo halogen anions and preferably contains chloride ions. The halogen or pseudo halogen concentration is typically at least 1M and may be 10 as high as 10M. The aqueous solution may also contain acid and is typically between 0.01 and 1M in acid, particularly hydrochloric acid. It will be appreciated that many of the metals which are present in the original aqueous solution can exist in more than one 15 valency state. The effectiveness of the solvent extraction process is dependent on the valency states of the various metals present in the aqueous solution. If conditions are adjusted such that any copper present exists essentially all in the divalent state, as a cupric salt, the solvent extraction process results in extraction of 20 copper and palladium with only very low levels of the other metals being extracted. The process of the present invention is believed to proceed by the formation of a complex, for example a halogeno complex, between the palladium, or copper, salt and the substituted 25 heterocyclic compound (the extractant), this complex being soluble in the organic phase. The formation of this neutral complex is believed to be reversible and, during the stripping stage or stages, the complex breaks down and the metal salt passes into the aqueous phase whilst the extractant remains in the organic phase which can 30 then be recycled to the solvent extraction stage. At the stripping stage, the organic phase containing the extractant and the extracted metals is contacted with an aqueous phase which may be water or a solution having a reduced metal or halogen or pseudo halogen, concentration whereby the metal is 35 transferred into the aqueous phase. 22 8 1 23 S.34667 In the stripping stage, stripping to remove copper is effected using water or a dilute acid as the stripping medium from which any copper which is present may be recovered by electrolysis. However, it will be appreciated that the recovery of copper in such a 5 system may not be viable commercially and hence, once the copper has been separated from the palladium, it may be discarded. The aqueous solution contains high levels of several metals including iron and it is important that the extractant should have good selectivity for palladium and copper over the other metals 10 including iron. The extractants used in the process of the present invention have this property. A yet further property which is of importance in the process of the present invention is the absence of significant protonation by the aqueous solution containing the platinum group metals. 15 Protonation of the extractant not only carries acid into the organic phase, building up unnecessary halide or pseudo halide concentration on the strip side, but is also believed to be associated with loss of selectivity for palladium and copper over other metals present in the aqueous solution, for example silver. Again the preferred 20 extractants of the present invention have excellent resistance to protonation even in contact with relatively acidic leach solutions. The process of the present invention can be effected using a wide range of substituted heterocyclic compounds as the extractant. We have obtained good extraction of palladium, together with copper, 25 from aqueous solutions containing platinum group metals together with other metals when using, as the extractant, the bis esters of pyridine-3,5-dicarboxylic acid, for example the bis-isodecyl ester; or other extractants such as an ester of pyrazine-2-carboxylic acid, for example the mixed branched octadecyl ester; an ester of 30 4-phenylpyrimidine-5-carboxylic acid, for example the mixed branched octadecyl ester; an ester of 1,2,4-triazole-l-carboxylic acid, for example the 2-octyldodecyl ester and an ester of benzimidazole-1-carboxylic acid, for example the mixed branched octadecyl ester. 22 8 1 24 S.34667 Particularly useful results are obtained when the substituted heterocyclic compound is a substituted pyridine compound and it is a particular aspect of the present invention to use, as the substituted heterocyclic compound, a bis ester of pyridine-5 3,5-dicarboxylic acid. The process of the present invention is effected by contacting an aqueous solution with a solution of the extractant in a water-immiscible organic solvent. Examples of suitable water-immiscible organic solvents are aliphatic, aromatic and alicyclic 10 hydrocarbons, chlorinated hydrocarbons such as perchloroethylene, trichloroethane and trichloroethylene. Mixtures of solvents may be used. Especially preferred in conventional hydrometallurgical practice are mixed hydrocarbon solvents such as high boiling, high flash point, petroleum fractions (for example kerosene) with varying 15 aromatic content. In general, hydrocarbon solvents having a high aromatic content, for example AROMASOL H which consists essentially of a mixture of trimethylbenzenes and is commercially available from Imperial Chemical Industries PLC (AROMASOL is a registered trade mark), provide a higher solubility for the extractant and the metal 20 complexes formed, whilst kerosene having a relatively low aromatic content, for example ESCAID 100 which is a petroleum distillate containing 20% aromatics, and which is commercially available from ESSO (ESCAID is a registered trade mark) may in certain cases improve the hydrometallurgical performance of the extractant. Factors 25 influencing the solubility of the extractant and its metal complexes are complicated, but in general extractants having highly branched substituents and/or an isomeric mixture of substituents have comparatively high solubility. The concentration of the extractant in the water-immiscible 30 organic solvent may be chosen to suit the particular aqueous solution to be treated. Typical values of extractant concentration in the organic phase are between about 0.1 to 2 Molar, and an especially convenient range is from 0.2 to 0.8 Molar in the organic solvent. 22 8 1 25 S.34667 The extraction stage and the strip stage of the solvent extraction process may conveniently take place at ambient temperature for example in the range 20 to 30°C. However it is possible to improve the metal transfer from the aqueous solution to the strip 5 solution if the extraction stage is operated at ambient temperature, whilst the strip stage is operated at elevated temperature, for example up to 70°C, especially up to 50°C. We have also found that the undesirable formation and build-up of oligomeric complexes of the extractant and the metal or metals may be alleviated if the strip 10 stage is operated at elevated temperatures, for example up to 70°C. The invention is illustrated by the following Examples in which all parts and percentages are by weight unless otherwise stated. Example 1 15 An organic solution of di-isodecylpyridine-3,5-dicarboxylate was prepared by dissolving the di-ester in ESCAID 100 (a petroleum distillate containing 20% aromatics) to give a concentration of 223g/dm3 of the di-ester in the solvent, which corresponds to a 0.5 Molar solution of the di-ester. The ester was prepared by the 20 procedure described in Example 11 of European Patent Specification 57797. The organic solution was used to extract palladium from an aqueous solution containing platinum group metals, and other metals, as their chlorides in a solution with a total chloride concentration 25 of lllg/dm3, corresponding to 3.13M in chloride ion and having a pH of 0.01. The extraction was effected using 30cm3 of the organic solution and 30cm3 of the aqueous solution. The solutions were contacted by vigorous stirring at 25°C for 30 minutes. The phases 30 were then allowed to separate. The original aqueous phase, the final aqueous phase and the final organic phase were analysed to determine the concentration of at least some of the metals therein. The results obtained are set out in Table One. 22 8 1 26 S.34667 Table One 5 Phase (a) Metal anc concentration (mg/dm 3) Cu Pd Pt Au Rh Ru Ir Pb Ni Fe a8 Orig.Aq. 7635 6920 90 20 335 400 22 965 4900 6065 40 Ext. Aq. 3990 885 ND ND ND ND ND ND ND ND ND Ext.Org. 4061 6315 2 4.5 <1 <2 <10 6 5 2 <1 10 Notes to Table One ND means Not Determined. (a) Orlg.Aq. means original aqueous phase. Ext.Aq. means the aqueous phase after being contacted with the organic phase. 15 Ext.Org. means the organic phase after being contacted with the aqueous phase. The aqueous phase after extraction (Ext.Aq.) was analysed only for copper and palladium since the analysis of the organic 20 extract (Ext.Org.) indicated that very little of the other metals had been extracted into the organic phase. Example 2 The procedure of Example 1 was repeated with the exception that a different aqueous solution was used which contained different 25 concentrations of the various metals with a total chloride concentration of 199g/dm3, corresponding to 5.6M in chloride ions, and having a pH of -0.22. The results obtained are set out in Table Two. 22 8 1 27 S.34667 Tab le Two Phase Metal and concentration (mg/dm3 ) (a) Cu Pd Pt Au Rh Ru Ir Pb Ni Fe a8 Orig.Aq. 73500 28000 44 12 1015 55 <20 3830 15500 1570 95 Ext.Aq. 62590 19270 ND ND ND ND ND ND ND ND ND Ext.Org. 9467 8040 <1 2.5 <1 <2 <10 8 8 11 <1 10 Notes to Table Two ND and (a) are both as defined in Notes to Table One. Example 3 The process of this example demonstrates the selective 15 stripping of copper and palladium from the organic solution of the extractant. The procedure of Example 1 was repeated with the exception that 60cm3 of the organic solution was contacted with 60cm3 of the aqueous solution. After separation of the aqueous and organic 20 phases, samples of each were filtered and the filtered solutions were analysed. A 40cm3 portion of the organic phase was then contacted with a 40cm3 portion of water by shaking vigorously for two minutes at 25°C. The aqueous phase was separated and the organic phase was 25 contacted with a further 40cm3 portion of water using the same procedure. The two aqueous phases were combined. Samples of both the organic and aqueous phases were analysed. A 20cm3 portion of the water stripped organic phase was contacted with a 20cm3 portion of an aqueous ammonia solution having 30 an ammonia content of 9% w/v. Contacting was effected by shaking vigorously at 25°C for 2 minutes. The two phases were separated and the organic phase was contacted with a further 20cm3 of the same aqueous ammonia solution using the same procedure. The two ammonia solutions were combined. Samples of the aqueous and organic 35 solutions were filtered and analysed. 22 8 1 28 S.34667 The results of the analyses of the various fractions at different stages are set out in Table Three. Table Three Phase (a)(b) Metal and Concentration (mg/dm3) Cu Pd Orig.Aq. 7635 6290 Ext.Org. 4035 5925 Water Wash 2033 <1 Washed Org. 1 5995 Ammonia ND 2815 Res.Org. ND 26 15 Notes to Table Three (a) is as defined in Notes to Table One. (b) Water Wash is the combined aqueous phase resulting from contacting the Ext.Org. with water. Washed Org. is the organic phase resulting from contacting the 20 Ext.Org. with water. Ammonia is the combined ammonia solutions resulting from contacting the Washed Org. with the ammonia solution. Res.Org. is the residual organic phase resulting from contacting the Washed Org. with the ammonia solution. 25 Example 4 The procedures described in Example 3 were repeated with the exception that the aqueous solution was a further sample of the solution used in Example 2. The results obtained are set out in 30 Table Four. 22 8 I 29 S.34667 Table Four Phase Metal and Concentration (mg/dm3) (a)(b) Cu Pd Orig.Aq. 73500 28000 Ext.Org. 9366 8655 Water Wash 4702 <1 Washed Org. 0.4 8758 Ammonia ND 4520 Res.Org. ND 30 Notes to Table Four (a) is as defined in Notes to Table One. 15 (b) is as defined in Notes to Table Three. It will be observed from Examples 3 and 4 that selective stripping to obtain copper and palladium essentially free from the other metal is possible. 20 Examples 5 to 10 The procedures described in Example 3 were repeated with the exceptions that the extraction stage was effected using 3 volumes of the organic solution to 1 volume of the aqueous solution containing platinum group metals, as used in Example 1, different substituted 25 heterocyclic compounds were used as the extractant and an ammonia solution containing 25% v/v of 880 ammonia was used. The concentration of the extractant in the organic solution was 0.5M in all cases. The results of the analyses of the various fractions at 30 different stages are set out in Table Five and Table Six. 22 8 1 30 S.3A667 Table Five Phase (c) Metal and concentration (mg/dm3) Example 5 Example 6 Example 7 PyE (d) PyE* (d)(e) PzE (f) Cu Pt Pd Cu Pt Pd Cu Pt Pd EA 2250 70 30 4035 45 15 6030 65 20 E0 1875 <10 2320 1480 <10 2600 645 <10 2465 WW 765 <5 <5 660 <5 <5 310 5 <5 WO <10 <10 2380 <10 <10 2590 <10 <10 2565 AM <5 <5 1170 <5 <5 1200 <5 <5 1220 RO <10 <10 15 <10 <10 25 <10 <10 <10 15 Table Six Phase Metal and concentration (mg/dm3) (c) Example 8 Example 9 Example 10 PrE (h) TzE* (e)(i) BzE (1) Cu Pt Pd Cu Pt Pd Cu Pt Pd EA 6535 70 70 470 70 15 1090 75 745 EO 435 <10 2480 2410 <10 2570 2345 <10 2205 WW 170 <5 <5 1000 <5 <5 1080 <10 <5 WO 45 <10 2315 150 <10 2625 <10 <5 1910 AM 15 <5 1115 80 <5 1810 <5 <5 1020 RO <10 <10 50 <10 <10 10 </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 22 8 1 31 S.34667 10 Notes to Table Five and Table Six (c) EA is Ext.Aq. as defined in Note (a) to Table One. EO is Ext.Org. as defined in Note (a) to Table One. WW is Water Wash as defined in Note (b) to Table Two. WO is Washed Org. as defined in Note (b) to Table Two. AM is Ammonia as defined in Note (b) to Table Two. RO is Res.Org. as defined in Note (b) to Table Two. (d) PyE is the pyridine ester used in Example 1. (e) * The organic solution was a solution of the extractant in AROMASOL H. (f) PzE is the mixed branched octadecyl ester of 15 pyrazine-2-carboxylic acid. (h) PrE is the mixed branched octadecyl ester of 4-phenylpyrimidine-5-carboxylic acid. 20 (i) TzE is l-(2'-octyldodecyloxycarbonyl)-l,2,4-triazole. (j) BzE is mixed branched 1-octadecyloxycarbonylbenzimidazole. 22 a 1 32 S.34667/ WHATtf/WE CLAIM IS:

1. A solvent extraction process for palladium values from aqueous solutions of palladium salts containing halide or pseudo 5 halide anion which comprises the steps of (1) contacting the aqueous solution containing palladium salts with a solution of an extractant in a water-immiscible organic solvent; (2) separating the aqueous solution from the solution of the extractant in the water-immiscible solvent into which palladium has been extracted; and (3) contacting 10 the resultant organic phase with an aqueous strip solution whereby the palladium transfers into the aqueous strip solution characterised in that the aqueous solution of palladium salts containing halide or pseudo halide anion is contacted with a solution in a water-immiscible organic solvent of an extractant which is a 15 substituted heterocyclic compound containing a single heterocyclic ring containing 1, 2 or 3 nitrogen ring atoms and one or more groups -COX which are linked directly to the heterocyclic ring or are linked to the heterocyclic ring through a group A, wherein

A is an optionally substituted methylene linking group, an 20 optionally substituted vinylene linking group or an optionally substituted phenylene linking group;

X is a group -OR1 or -NR2R3;

.1

is a hydrocarbyl group or substituted hydrocarbyl group containing from 5 to 36 carbon atoms; and

2 3

25 R and R which may be the same or different, are hydrogen or a hydrocarbyl group or a substituted hydrocarbyl group, and in each group -36 carbon atoms

2 3 2 3

in each group -NR R , R and R together contain from 5 to

30

2. A process as claimed in claim 1 wherein the aqueous solution of palladium salts is either one which has been obtained from a palladium-containing catalyst and contains other metals also present in the catalyst or as contaminants, or is a solution containing platinum group metals.

22 8 1 o

33 S.34667/

3. A process as claimed in either claim 1 or claim 2 wherein the substituted heterocyclic compound is of the general formula:

5 Het [(A) (COX) ]

a y n.

where A and X are as hereinbefore defined;

Het is, or contains, a single heterocyclic ring containing 1, 2 or 3 nitrogen ring atoms and the group or groups -(A)a(COX)^ 10 are linked to the ring atoms of the heterocyclic ring;

a is 0 or 1;

n is at least one up to the maximum number of free valencies in the heterocyclic ring; and y is from 1 up to 3.

15

4. A process as claimed in claim 3 wherein the substituted heterocyclic compound is one in which the free valencies which are not occupied by a group -(A) (COX) are occupied either by a hydrogen a y atom or a substituent group Y,

20 wherein

Y is selected from halogen, alkyl, aryl, alkoxy, aryloxy, aralkyl, alkaryl, cyano, nitro or carboxylic acid.

5. A process as claimed in claim 4 wherein the group Het is a 25 single heterocyclic ring fused with a non-heterocyclic ring which may be unsubstituted or substituted with at least one group Y.

6. A process as claimed in any one of claims 1 to 5 wherein the

12 3

substituents in the substituted hydrocarbyl groups R , R or R are 30 one or more of halogen, nitro, cyano, hydroxy, alkoxy, aryloxy, alkoxycarbonyl and alkylcarbonyloxy.

35

7. A process as claimed in any one of claims 2 to 6 wherein the aqueous solution containing palladium salts contains at least platinum and palladium.

22 8 1

34 S.34667/

8. A process as claimed in any one of claims 1 to 7 wherein the aqueous solution contains platinum group metal salts and also contains a salt of at least one metal selected from iron, nickel,

5 copper, silver and gold.

9. A process as claimed in any one of claims 1 to 8 wherein the substituted heterocyclic compound is one containing at least two -COX groups and the group X in each of the groups -COX is different.

10

10. A process as claimed in any one of claims 3 to 9 wherein the substituted heterocyclic compound contains a group A which is a vinylene linking group which contains no substituents other than the groups -COX.

15

11. A process as claimed in claim 10 wherein the vinylene linking group contains two groups -COX, one on each carbon atom of the vinylene linking group.

20 12. A process as claimed in any one of claims 1 to 11 wherein the group X is a group -OR1 and R1 is an alkyl group containing from 8 to 24 carbon atoms.

13. A process as claimed in claim 12 wherein R1 is a branched 25 chain alkyl group containing from 9 to 24 carbon atoms.

14. A process as claimed in claim 13 wherein R1 is of the general formula:

30 /r6

- CH, - CH

^ R7

where

35 R^ and R are alkyl groups and may be the same or different.

22 8 1

35 S.34667/

15.

A process as claimed in any one of claims 1 to 14 wherein

.1

each R is a mixture of isomers.

16.

A process as claimed in any one of claims 1 to 11 wherein

2 3

X is a group -NR R ;

2

R is hydrogen; and

3

R is a branched chain alkyl group.

10

17. A process as claimed in any one of claims 1 to 4, 6 to 8

and 12 to 16 wherein the extractant is a substituted pyridine of formula:

15

or

00.

^•N

COX

where X and Y are as defined; and 20 x is zero or an Integer from 1 to 4.

18. A process as claimed in any one of claims 1 to 4, 6 to 9

and 12 to 16 wherein the extractant is a substituted pyridine of the formula:

25

30

(COX)

wherein

X n

1 2 3

is a group -OR or -NR R ;

is 2 or 3;

22 8 1

36 S.34667/

each R1 which may be the same or different, is an alkyl group and together the groups R1 contain a total of from 16 to 36 carbon atoms;

2 3

each R and R which may be the same or different, is an alkyl group

5 and the total number of alkyl carbon atoms contained

2 3

in all the respective groups R and R is from 20 to 70;

z is zero or an integer from 1 up to (5-n); and each Y which may be the same or different, is one or more of 10 the substituents halogen, alkyl, aryl, alkoxy,

aryloxy, aralkyl, cyano, nitro or carboxylic acid.

19. A process as claimed in either claim 17 or 18 wherein x or z is at least one and at least one of the groups Y is a carboxylic acid

15 group.

20. A process as claimed in any one of claims 1 to 4, 6 to 9 and 12 to 16 wherein the extractant is a substituted pyrimidine, pyrazine or pyridazine of the formula:

20

(cox)n

25

30 N

G

oob (- -H — (COX),

37

22

S.34667/

00,

(COX)

wherein X and Y are both as defined;

n is 1, 2 or 3; and 10 b is zero or an integer from 1 up to (4-n).

21. A process as claimed in claim 20 wherein the extractant is one in which at least one position ortho to one of the two nitrogen atoms is free from any substituent.

15

22. A process as claimed in claim 21 wherein the extractant is one in which both positions ortho to one of the two nitrogen atoms are free from any substituent.

20 23. A process as claimed in any one of claims 20 to 22 wherein n is two and the extractants are alkyl esters of 4,5-dicarboxy-pyrimidine, 2,6-dicarboxypyrazine or 4,5-dicarboxypyridazine.

24. A process as claimed in any one of claims 20 to 22 wherein 25 n is one and the extractant is a substituted pyrimidine in which the group -COX is located in the 5-position in the pyrimidine ring.

25. A process as claimed in claim 24 wherein the substituted pyrimidine has a substituent Y in the 4- or 6-position.

30

26. A process as claimed in any one of claims 20 to 22 wherein n is one and the extractant is a substituted pyrazine having the group -COX in the 2-position and in substituent Y in the 6-position in the pyrazine ring.

22 8 1

38 S.34667/

27. A process as claimed in any one of claims 20 to 26 wherein the group R1 is derived from a branched secondary or tertiary alcohol.

5

28. A process as claimed in any one of claims 1 to 4, 6 to 8 and 10 to 16 wherein the extractant is a substituted triazole of the formula:

10 N N - (A) (COX)

U

where A, X and a are all as defined; and 15 m is from 1 to 3.

29. A process as claimed in claim 28 wherein the extractant is of the formula:

20 N N - COOR1 or N N - C0NR2R3

12 3

where R , R and R are all as defined.

22 8 1

39 S.34667/

20

25

30. A process as claimed in claim 28 wherein the extractant is of the formula:

A1 A2 I '

N N - C = C - COX

10 where X is as defined; and

1 2

A and A are hydrogen or s nitro, lower alkyl or the group -COX.

1 2

A and A are hydrogen or substituents selected from halogen, cyano,

31. A process as claimed in claim 30 wherein A1 is a group -COX

2

15 and A is hydrogen, and X is the same in both groups -COX.

32. A process as claimed in any one of claims 28 to 31 wherein X

is a group -OR1 in which the group R1 is derived from a secondary alcohol.

33. A process as claimed in any one of claims 1 to 8 and 12

to 16 wherein the extractant is a N-substituted 1,3-diazole of the formula:

30 wherein X is as defined;

g

R is hydrogen or an optionally substituted lower alkyl group or an optionally substituted vinyl group; and

D and Z, which may be the same or different, are separately hydrogen, an optionally substituted hydrocarbon group, a halogen, a nitro

10

15

22 8 1 o 1

40 S.34667/

group, a cyano group or a carboxylic ester group, or where D and Z both together with the two carbon atoms joining them form an optionally substituted aromatic or aliphatic cyclic group.

5

34. A process as claimed in claim 33 wherein the extractant is a benzimidazole of the formula:

g where R , X and Y are all as defined; and c is zero or from 1 up to 3.

35. A process as claimed in either claim 33 or claim 34 wherein the total number of alkyl carbon atoms in all substituents is from 9 to 30.

20

36. A process as claimed in either claim 33 or claim 34 wherein g

R is hydrogen or methyl; Y, or D and Z, contain at most one alkyl carbon atom; and R1 contains 9 to 24 carbon atoms.

37. A process as claimed in any one of claims 33 to 36 wherein

25 R1 is derived from a secondary alcohol.

38. A process as claimed in any one of claims 4 to 18, 20

to 23, 27 and 34 to 36 wherein the extractant contains no substituent groups Y.

25

22 8 1 o 1

41 S.34667/

39. A process as claimed in any one of claims 1 to 38 wherein the aqueous solution containing palladium salts also contains a copper salt, in stage (1) copper is also extracted into the solution 5 of the extractant and stage (3) is effected in two steps and in the first step (a) the organic phase is contacted with water or an aqueous acid and in the second step (b) the residual organic phase is contacted with an aqueous ammonia solution.

10 40. A process as claimed in claim 39 wherein copper is stripped from the organic phase in step (3a) to give an organic phase containing palladium and essentially free of copper.

41. A process as claimed in either claim 39 or claim 40 wherein 15 palladium is stripped from the residual organic phase in step (3b)

and is recovered from the aqueous ammonia solution.

42. A process as claimed in any one of claims 39 to 41 wherein in step (3b) the aqueous ammonia solution has an ammonia content of 2

20 to 20% w/v.

43. A process as claimed in any one of claims 1 to 42 wherein the aqueous solution containing palladium salts contains chloride ions.

44. A process as claimed in any one of claims 1 to 43 wherein the halogen or pseudo halogen concentration in the aqueous solution containing palladium salts is from 1M to 10M.

30

45. A process as claimed in any one of claims 1 to 44 wherein the aqueous solution containing palladium salts contains an acid at a concentration of from 0.01M to 5M of acid.

?2 8 1

42 S.34667/

46. A process as claimed in any one of claims 1 to 44 wherein the aqueous solution containing palladium salts contains copper, essentially all in the divalent state.

5

47. A process as claimed in any one of claims 1 to 4, 7, 8, 12 to 16 and 39 to 46 wherein the extractant is a bis-ester of pyridine-3,5-dicarboxylic acid; the mixed branched octadecyl ester of pyrazine-2-carboxylic acid; the mixed branched octadecyl ester of

10 4-phenylpyrimidine-5-carboxylic acid; l-(2'-octyldodecyloxy-

carbonyl)-l,2,4-triazole or mixed branched octadecyloxycarbonyl-benzimidazole.

48. A process as claimed in any one of claims 1 to 47 wherein 15 the water-immiscible organic solvent is an aliphatic, aromatic or alicyclic hydrocarbon or a chlorinated hydrocarbon.

49. A process as claimed in claim 48 wherein the water-Immiscible organic solvent is a mixture of hydrocarbon

20 solvents.

50. A process as claimed in any one of claims 1 to 49 wherein the concentration of the extractant in the water-immiscible organic solvent is between 0.1 and 2 Molar.

25

51. A process as claimed in any one of claims 1 to 50 wherein the extraction stage is effected at ambient temperature.

52. A process as claimed in any one of claims 1 to 51 wherein 30 the strip stage is effected at an elevated temperature of up to 70°C.

-43-

%L&lo<

53. A solvent extraction process as claimed in any one of claims 1 to 52 substantially as herein described with reference to any Example thereof.

&C>

By Hie/fheir authorised Agsnt A. J. PARK & SOW Per;

"T £ N

o\

;."V

I* * may & 90^

</div>